The vulnerability is caused by a buffer overflow condition in the Cisco SSH implementation. When a client attempts to authenticate using keyboard-interactive authentication, the server does not properly validate the length of the authentication request. This allows an attacker to send a specially crafted request that overflows the buffer, potentially allowing the attacker to execute arbitrary code on the server.
Because version strings are largely static across broad ranges of firmware revisions, an exposed Cisco-1.25 engine may be susceptible to multiple high-impact attacks depending on its explicit patching level.
Example fixed banner after upgrade:
The SSH protocol begins with a server identification string (RFC 4253, section 4.2): ssh-2.0-cisco-1.25 vulnerability
Check if device is end-of-life (most are).
The SSH-2.0-Cisco-1.25 vulnerability is a serious security flaw that affects certain versions of Cisco's SSH implementation. Administrators should take immediate action to mitigate the vulnerability by upgrading to a patched version, disabling keyboard-interactive authentication, or implementing additional security measures. By understanding the technical details of the vulnerability and taking proactive steps to prevent exploitation, administrators can help protect their systems and prevent similar vulnerabilities in the future.
The "ssh-2.0-cisco-1.25 vulnerability" is not a single bug but rather a . It tells a story: a Cisco device deployed years ago, likely stable, and forgotten by security teams. While the banner itself does not guarantee compromise, it dramatically increases the attack surface. The vulnerability is caused by a buffer overflow
While a banner itself is not a flaw, exposing SSH-2.0-Cisco-1.25 allows attackers to fingerprint the device. Network scanning engines like Shodan and Censys have indexed hundreds of thousands of internet-facing devices broadcasting this exact banner, identifying them as potential targets for multiple critical SSH-related vulnerabilities. Anatomy of the Vulnerabilities Affecting Cisco-1.25
The SSH-2.0-Cisco-1.25 banner has accompanied several distinct security issues. These can be broadly categorized into a few key areas.
A critical vulnerability (CVSS 9.9) was also discovered in the SSH subsystem of Cisco ASA and Firepower Threat Defense (FTD) Software. This issue, due to insufficient input validation, allowed an authenticated, remote attacker to execute commands on the underlying operating system with by sending crafted input during SSH sessions. Because version strings are largely static across broad
implementation allows a remote attacker to bypass authentication. By using a crafted private key, an attacker could log in with the privileges of the targeted user or the Virtual Teletype (VTY) line.
If an upgrade is not immediately possible, you can harden the existing configuration by disabling weak algorithms and key exchanges: